This invention relates to polymer latices and the use of such latices in coating and binder compositions such, for example, as paints, adhesives, paper coating and textile coating, the term "latex" being used herein in a broad sense to designate any, generally aqueous, dispersion of a water-insoluble polymer, the polymer being present in the form of particles.
Coating compositions based on high polymer latices, such as those mentioned above, are widely used in protective and decorative applications and have many advantages such as durability, abrasion resistance, ease of handling and application. However, although the dry adhesion of these coatings to most substrates is adequate, wet adhesion is frequently inadequate, particularly when the coatings are applied on certain difficult surfaces. A familiar example of poor wet adhesion is the unsatisfactory performance of most emulsion paints when these are applied over old alkyd or oil gloss paint. Under conditions of high humidity, such as may occur in kitchens and bathrooms, water vapour may penetrate the emulsion paint film and when the interface between the two paint surfaces becomes wet, adhesion failure may take place. Similarly, binder compositions based on said latices, whilst generally displaying good dry adhesion properties, do not generally have adequate wet adhesion characteristics.
Several modifications of high polymer latices have been proposed to give improved wet adhesion, but in most cases the extent of the improvements is much less than is necessary and even when an adequate increase in adhesion is obtained, there may be objections to the modification. For instance, according to British Patent No. 1,088,105, it is possible to obtain greatly enhanced wet adhesion by treating certain latices with ethylenimine, but the handling of this very toxic chemical is extremely hazardous, and side reactions of the ethylenimine with acetaldehyde produced by the hydrolysis of vinyl acetate monomer may lead to an unacceptable discolouration in polyvinyl acetate latices.
It has been proposed to improve the dry adhesion of coating compositions for certain substrates by incorporating polar groups, e.g. carboxyl, amido, hydroxyl, glycidyl and ureido groups, into the basic polymer of the latex. However, none of these groups (apart, possibly, from the ureido group) gives any appreciable increase in wet adhesion.